1. Field of the Disclosure
The present disclosure relates to a connecting structure for a secondary battery, and more particularly, to a connecting structure for a secondary battery, which connects the secondary battery to a protection circuit module, and a secondary battery pack including the same.
2. Description of the Related Art
Along with the technical development and increased demands of mobile devices, secondary batteries are used more and more as an energy source. Among them, lithium (ion/polymer) secondary batteries with high energy density, high operation voltage and excellent preservation and life characteristics are widely used as energy sources of various electronic products as well as various mobile devices.
Such secondary batteries may be used as a single battery cell or a battery pack where a plurality of unit cells are electrically connected to each other, depending on the kind of external device used. For example, a small-sized device such as a cellular phone may operate for a predetermined time with the power and capacity of a single battery cell, but middle-sized or large-sized devices such as notebooks, portable DVD, electric vehicles and hybrid vehicles demand the use of a battery pack in order to ensure large power and capacity.
Such a battery pack generally has a ‘soft pack’ structure, which is prepared by connecting a protection circuit or the like to a ‘core pack’ having a plurality of unit cells connected in series or in parallel, packed in a hard case. In a case where the unit cell employs a rectangular or pouch-type battery, unit cells are stacked so that wide surfaces face each other, and then electrode terminals of the unit cells are connected to each other by using a connection member such as a bus bar. Therefore, in case of preparing a cubic battery pack with a hexahedral structure, the rectangular or pouch-type batteries are advantageous as the unit cells.
Meanwhile, although a cylindrical battery generally has a higher electric capacity in comparison to a rectangular or pouch-type, a cylindrical battery may not easily stack due to its appearance. However, if the battery pack has a linear or plate shape as a whole, the cylindrical battery may have a more structural advantage than the rectangular or pouch-type battery.
Therefore, in the case of notebooks or portable DVDs, a battery pack is configured with a core pack, in which a plurality of cylindrical batteries is connected in series or in parallel. Such a core pack generally uses a 2P (parallel)-3S (series) linear structure, a 2P-3S plate structure, a 2P-4S linear structure, a 2P-4S plate structure or the like.
A parallel-type connection structure is configured by arranging two or more cylindrical batteries to be adjacent to each other in a lateral direction with the electrodes being arranged in the same direction, and then welding the cylindrical batteries by using a connection member. This parallel-type cylindrical battery is also called a ‘bank’.
A series-type connection structure is configured by arranging two or more cylindrical batteries in a long length so that electrode terminals with opposite polarities are successively located or by arranging two or more batteries to be adjacent to each other in their lateral direction in a state where electrode terminals are oriented toward opposite directions, and then welding the cylindrical batteries by using a connection member. As a connection member for electrical connection of such cylindrical batteries, a thin metal plate such as a nickel plate is generally used.
Meanwhile, since such a secondary battery contains various combustible materials therein, the secondary battery may heat or explode due to overcharge, overdischarge and other external physical impacts, making it very unstable. Therefore, a PCM (Protection Circuit Module) made of a PCB substrate is connected to the core pack of the battery pack in order to effectively control abnormal states such as overcharge and overdischarge.
FIG. 1 is a perspective view schematically showing a conventional battery pack. For the sake of easy understanding, FIG. 1 shows a coupling relation between a core pack and a protection circuit module in an exploded view, in which a pack case is not depicted.
As shown in FIG. 1, three electrode pairs of unit cells 11 connected to each other in parallel are connected in series by means of metal plates 20 to form a core pack 10. The metal plates 20 connected to the unit cells 11 of the core pack 10 are electrically connected to a protection circuit module 30 by means of soldering or welding.
However, the soldering or welding process for the core pack 10 and the protection circuit module 30 has the following problems. In detail, the welding or soldering process requires the skilled techniques and know-how of workers, and parameters for determining the intensity of welding should be continuously maintained, resulting in complicated and expensive production processes and serving as a factor that deteriorates the production efficiency. In addition, in the soldering or welding process for the core pack 10 and the protection circuit module 30, a short circuit may occur at the connection portion due to vibrations of the battery pack or an external impact, and an electric or thermal damage may be applied to the interface with the metal plate 20, which may become factors that threat the safety of the battery and increase the inferiority of products. In addition, the sequence of operation should be strictly obeyed during the soldering or welding process for the core pack 10 and the protection circuit module 30. If not, a great voltage is abruptly applied from the core pack 10 to the protection circuit module 30, which may damage the internal circuit of the protection circuit module 30 and cause malfunction. In particular, when there is a defect with a part of the unit cells or the protection circuit module 30 during the production process or in use, there is a disadvantage in that all components of the battery pack must be discarded.
Therefore, there is an urgent need for a technique capable of substituting a connection method using welding, soldering or the like, which demands dangerous and complicated work procedures, and allows easy connection and separation of the core pack 10 and the protection circuit module 30 while ensuring stability so that components of a battery pack may be partially reused, exchanged or repaired.